Ultrapure helium is, in particular, used in the electronics industry, for keeping at a constant temperature and cooling wafers supporting integrated circuits forming memories or processors.
The increase in the dimensions of wafers and the reduction in the thickness of the successive layers constituting the integrated circuits have resulted in a growing requirement as regards the purity of the helium used. In Europe, the current requirement for some applications is a content of the order of ppb (parts per billion) for each type of impurity (hydrogen, neon, other rare gases, nitrogen, etc.) in helium.
The conventional processes for purifying helium consist in passing helium in the gas state and at high pressure (10 to 200 bar), stored in bottles or in tubes, through a cryogenic purifier containing an adsorbent generally cooled to approximately 80 K (physical adsorption) or a getter at room temperature (chemisorption of impurities other than neutral gases).
This technique is unsatisfactory because, on the one hand, storing helium gas requires much space and, on the other hand, it is necessary to use a plurality of adsorbers in series for trapping the gaseous impurities, which also takes up space and is furthermore expensive.